Transparent conductors, such as Indium Tin Oxide (ITO), combine the electrical conductivity of metal with the optical transparency of glass and are useful as components in electronic devices, such as in display devices. Flexibility is likely to become a broader challenge for ITO, which does not seem well suited to the next generation of display, lighting, or photovoltaic devices. These concerns have motivated a search for replacements using conventional materials and nanomaterials. There is variety of technical approaches for developing ITO substitutes and there are four areas in which the alternative compete: price, electrical conductivity, optical transparency, and physical resiliency.
Electrically conductive polymers, such as polythiophene polymers, particularly a polymer blend of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate) (“PEDOT-PSS”) have been investigated as possible alternatives to ITO. The electrical conductivity of electrically conductive polymers is typically lower than that of ITO, but can be enhanced through the use of conductive fillers and dopants.
Processes for making electrically conductive metal nanostructures are known. Ducamp-Sanguesa, et. al., Synthesis and Characterization of Fine and Monodisperse Silver Particles of Uniform Shape, Journal of Solid State Chemistry 100, 272-280 (1992) and U.S. Pat. No. 7,585,349, issued Sep. 8, 2009, to Younan Xia, et. al., each describe synthesis of silver nanowires by reduction of a silver compound in a glycol in the presence of polyvinylpyrrolidone.
Structures comprising a network of silver nanowires encapsulated in an electrically conductive polymer have been described. U.S. Patent Application Publication No. 2008/0259262 describes forming such structures by depositing a network of metal nanowires on a substrate and then forming a conductive polymeric film in situ, e.g., by electrochemical polymerization using the metal nanowire network as an electrode. U.S. Patent Application Publication No. 2009/0129004 describes forming such structures by filtration of a silver nanowire dispersion to form a silver nanowire network, heat treating the network, transfer printing the heat treated network, and encapsulating the transfer printed network with polymer.
The performance of such electrically conductive polymer or silver nanowire composite films is, in some cases, comparable to that of ITO but the processing required to obtain composite films that exhibit that level of performance is quite demanding, for example, the above described films require processing steps, such as thermal treatment and compression, in order to ensure that sufficient electrical connections are made among the electrically conductive nanowires of the composite film to provide a film having high conductivity and transparency.